U.S. patent number 5,118,378 [Application Number 07/751,677] was granted by the patent office on 1992-06-02 for apparatus for detecting an end point of etching.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Tetsunori Kaji, Gen Marumoto, Tatsuo Moroi, Yuzou Ohhirabaru, Keiji Tada, Noriaki Yamamoto.
United States Patent |
5,118,378 |
Moroi , et al. |
June 2, 1992 |
Apparatus for detecting an end point of etching
Abstract
A method of detecting an end point of etching by emission
spectroscopy. Using a constant ratio between emission intensities
in the course of etching and after the termination thereof, a
correction value is computed with data of a waveform already
adjusted to be capable of detecting an end point of etching and the
corresponding emission intensity in the course of etching treatment
thereafter, and the waveform of corresponding emission intensity in
the course of etching treatment is processed so that the detection
can be conducted on the same level as in the end point detection
already adjusted to be capable of detecting the end point of
etching at the time of treatment. Thus, irrespective of the
reduction of the quantity of emission for an emission detection at
each time of treatment, a constant electric signal of the same
detecting level can be obtained, making it possible to detect an
end point of etching with the same accuracy as in the initial
treatment.
Inventors: |
Moroi; Tatsuo (Kudamatsu,
JP), Tada; Keiji (Kudamatsu, JP), Yamamoto;
Noriaki (Kudamatsu, JP), Kaji; Tetsunori
(Kudamatsu, JP), Marumoto; Gen (Kudamatsu,
JP), Ohhirabaru; Yuzou (Kudamatsu, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
27024438 |
Appl.
No.: |
07/751,677 |
Filed: |
August 23, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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419312 |
Oct 10, 1989 |
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Current U.S.
Class: |
156/345.25;
204/192.33; 204/298.32; 356/306; 356/316; 422/52; 422/98 |
Current CPC
Class: |
H01J
37/32963 (20130101); H01J 37/32935 (20130101) |
Current International
Class: |
H01J
37/32 (20060101); C23F 001/02 () |
Field of
Search: |
;156/345,626,627,643
;422/52,83,98 ;356/72,306,316 ;364/498 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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57-169241 |
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Oct 1982 |
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JP |
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59-113625 |
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Jun 1984 |
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JP |
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60-060712 |
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Apr 1985 |
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JP |
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62-65424 |
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Mar 1987 |
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JP |
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62-93940 |
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Apr 1987 |
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JP |
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62-93943 |
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Apr 1987 |
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JP |
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62-128124 |
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Jun 1987 |
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JP |
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62-165920 |
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Jul 1987 |
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JP |
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63-10523 |
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Jan 1988 |
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JP |
|
63-107026 |
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May 1988 |
|
JP |
|
63-178527 |
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Jul 1988 |
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JP |
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63-254732 |
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Oct 1988 |
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JP |
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63-303086 |
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Dec 1988 |
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JP |
|
1181424 |
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Jul 1989 |
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JP |
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1-226153 |
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Sep 1989 |
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JP |
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1235336 |
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Sep 1989 |
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JP |
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Primary Examiner: Wityshyn; Michael G.
Assistant Examiner: Bruckner; John J.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus
Parent Case Text
This application is a continuation of Ser. No. 07/419,312, filed on
Oct. 10, 1989, now abandoned.
Claims
What is claimed is:
1. An etching end point detecting apparatus detecting an end point
of etching in an etching apparatus performing an initial etching
treatment and a subsequent etching treatment, the etching end point
detecting apparatus comprising:
a photoelectric converter detecting an optical emission from the
etching apparatus during the first etching treatment and the
subsequent etching treatment and converting the detected optical
emission to an emission intensity signal;
a subtracter receiving the emission intensity signal from the
photoelectric converter and subtracting an adjustable offset value
from the received emission intensity signal, thereby producing an
offset emission intensity signal;
an amplifier receiving the offset emission intensity signal from
the subtracter and amplifying the received offset emission
intensity signal by an adjustable gain value, thereby producing a
correct emission intensity signal;
etching end point detecting means receiving the corrected emission
intensity signal from the amplifier and detecting an end point of
etching of the initial etching treatment and an end point of
etching of the subsequent etching treatment from the received
corrected emission intensity signal;
an initial offset value setter setting an initial offset value
Voff1, outputting the set initial offset value Voff1, and setting
the offset value of the subtracter to the outputted initial offset
value Voff1 in the initial etching treatment;
an initial gain value setter setting an initial gain value G1,
outputting the set initial gain value G1, and setting the gain
value of the amplifier to the outputted initial gain value G1 in
the initial etching treatment;
storage means receiving the emission intensity signal from the
photoelectric converter, the initial offset value Voff1 from the
initial offset value setter, and the initial gain value G1 from the
initial gain value setter; storing an emission intensity value Va1
of the received emission intensity signal at a predetermined time
t1 in the initial etching treatment; storing the received initial
offset value Voff1 and the received initial gain value G1; and
outputting the stored emission intensity value Va1, the stored
initial offset value Voff1, and the stored initial gain value
G1;
ration computing means receiving the emission intensity value Va1
from the storage means and the emission intensity signal from the
photoelectric converter, computing an emission intensity value
ratio Va1/Van from the received emission intensity value Va1 and an
emission intensity value Van of the received emission intensity
signal at a predetermined time t1 in the subsequent etching
treatment, and outputting the computed emission intensity value
ratio Va1/Van;
corrected value computing means receiving the emission intensity
value ratio Va1/Van from the ratio computing means and the initial
gain value G1 from the storage means; computing a corrected gain
value Gn from the received emission intensity ratio Va1/Van and the
received initial gain value G1 in accordance with the expression
Gn=(Va1/Van).times.G1; computing a corrected offset value Voffn
from the computed corrected gain value Gn, the emission intensity
value Van, and an emission intensity value Vf1 of the corrected
emission intensity signal at the predetermined time t1 in the
initial etching treatment in accordance with the expression
Voffn=Van-(Vf1/Gn); outputting the computed corrected offset value
Voffn and the computed corrected gain value Gn; and setting the
offset value of the subtracter to the outputted corrected offset
value Voffn and the gain value of the amplifier to the outputted
corrected gain value Gn during the subsequent etching
treatment.
2. An etching end point apparatus according to claim 1, wherein the
etching apparatus is an etching apparatus performing the initial
etching treatment and the subsequent etching treatment such that
the initial etching treatment and the subsequent etching treatment
are one type of etching treatment.
3. An etching end point apparatus according to claim 1, wherein the
etching apparatus is an etching apparatus performing a multi-step
etching treatment including a plurality of different types of
etching treatments and performing the initial etching treatment and
the subsequent etching treatment such that the initial etching
treatment and the subsequent etching treatment are different types
of etching treatments.
4. An etching end point apparatus according to claim 1, wherein the
etching apparatus is an etching apparatus performing a plurality of
different types of etching treatments and performing the initial
etching treatment and the subsequent etching treatment such that
the initial etching treatment and the subsequent etching treatment
are one type of etching treatment.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of and an apparatus for
detecting an end point of etching, and more particularly to a
method of and an apparatus for detecting by emission spectroscopy
an end point of etching of a specimen, such as the substrate of a
semiconductor device, to be etched by plasma treatment.
2. Description of the Invention
As an apparatus for detecting by emission spectroscopy an end point
of etching of a specimen such as the substrate of a semiconductor
device to be etched by plasma treatment, there is known, for
example, one which is disclosed in Japanese Patent Laid-Open No.
303086/1988. According to this conventional art, an electric output
signal from a photoelectric converter is stored as a standard
signal in a storage of normal emission in a storage when the
cloudiness of a window member is within a permissible range. A
member of monitoring the state of the cloudiness compares an actual
signal from the photoelectric converter with the standard signal
and generates an output corresponding to the result of such
comparison. Based on this output signal, a signal for the required
correction will be transmitted to the member of detecting an end
point of etching. Thus, even when the level of the output signal
from the photoelectric converter to the member of detecting an end
point of etching is lowered because of the cloudiness of the window
member, the end point of the etching treatment can be detected
while correction is being made for the member to detect an end
point of etching. Thus, the detection of an end point thereof is
carried out accurately.
In this conventional art, however, nothing has been disclosed as to
how the actual signal of the photoelectric converter can be
compared with the standard signal to obtain a signal to instruct
correction. How the signal to instruct correction is added to the
member of detecting an end point of etching has not been disclosed,
either. Also, this conventional art describes that even when the
level of the signal output of the photoelectric converter to the
member to detect an end point of etching is lowered because of the
cloudiness of the window member, the end point of etching treatment
can be detected while correction is being made for the member to
detect an end point of etching. However, if the end point of
etching treatment must be detected while correction is being made
for the member to detect the end point thereof, there may be a fear
that an accurate detection of the end point of etching becomes
impossible depending on some case where a treatment time for
etching is, for example, very short requiring the immediate
detection of an end point of etching. In such case, the end point
thereof has come while correction is still being made. In other
words, the end point thereof may have been detected before a final
correction was still to be made. Also, since the end point of
etching is detected while correction is being made, there arises
the problem of a delay in the treatment time.
In addition to this conventional art, there are known ones using
emission spectroscopy for detecting an end point of etching which
are disclosed in Japanese Patent Laid-Open No. 65424/1987 and
Japanese Patent Laid-Open No. 165920/1987.
The conventional art disclosed in Japanese Patent Laid-Open No.
65424/1987 describes that while etching a specimen, the first
waveform of emission intensity and a waveform n thereof are
compared with each other without any correction at each time, and
with the differential value thus obtained, those of n+1 are
corrected, making it easier to carry out the detection of an end
point of etching. However, according to this conventional art,
there arises a problem of affecting accuracy adversely because the
correction should be made in the next treatment in accordance with
the previous data.
Another conventional art disclosed in Japanese Patent Laid-Open No.
165920/1987 describes that a signal at the time of previous
treatment is compared with an input signal, and if there is any
differential value between them, the value of the electric signal
will be adjusted to be identical to the signal at the time of
previous treatment, by changing a gain value of the photoelectric
converter so that any detection of an end point of etching in the
same process can be conducted by the same detecting value even when
the quantity of emission collected by the photoelectric converter
is changing because of the cloudiness of the observation window or
the like. However, this conventional art will result in a delay in
the time between the output signal transmitted by the comparing
function and the response thereto by an adjustment function.
Furthermore, there are known ones concerning the apparatus of this
kind, which are disclosed in Japanese Patent Laid-Open No.
60772/1985, Japanese Patent Laid-Open No. 93940/1987, Japanese
Patent Laid-Open No. 128124/1987, U.S. Pat. No. 4,615,761, Ser. No.
07/000,368 and others.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a method
of and an apparatus for detecting an end point of etching in which
an initial detection of the end thereof can be easily conducted
even when the quantity of emission collected from an emission
detector becomes smaller due to a repetitive etching treatment.
To attain the primary object of the present invention, there is
provided an apparatus for detecting an end point of etching by
emission spectroscopy in a repetitive etching treatment, which
comprises a means of computing correction in accordance with the
data obtainable in the course of the subsequent etching treatment
by utilizing the constant ratio of the emission intensities in the
course of etching and after the termination thereof in an etching
treatment, and an apparatus having a means of adjusting a waveform
of the corresponding emission intensity in said etching treatment
so as to conduct the detection on the same detecting level as in
the detection at the time of initial treatment, and a method of
adjusting the waveform of the corresponding emission intensity in
the course of said etching treatment so as to conduct a detection
on the same detecting level at the time of initial treatment by
computing correction in accordance with the data obtainable at the
time of initial treatment and the corresponding emission intensity
in the course of the subsequent etching treatment. Thus,
irrespective of the quantity of emission of each detection which
decreases at each time of the treatment, a constant electric signal
is obtainable on the same detecting level, making it possible to
conduct easily the detection of an end point of etching as
accurately as the one at the time of initial treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an apparatus for detecting
an end point of etching in the first embodiment of the present
invention,
FIG. 2(a) is a diagram representing the waveform of an electric
signal converted by a photoelectric converter at the time of first
treatment,
FIG. 2(b) is a diagram representing the waveform of an electric
signal converted by the photoelectric converter at the time of n
treatment,
FIG. 3 is a diagram representing the waveform of an electric signal
corrected at the time of first treatment,
FIG. 4 is a diagram representing the waveform of an electric signal
amplified from the electric signal previously corrected at the time
of n treatment as it is,
FIG. 5 is a diagram representing the waveform corrected by the
present invention at the time of n treatment,
FIG. 6 is a flow chart representing the function of the apparatus
shown in FIG. 1,
FIG. 7 is a block diagram illustrating the apparatus for detecting
an end point of etching in the second embodiment of the present
invention,
FIG. 8 is a flow chart representing the function of the apparatus
shown in FIG. 7,
FIG. 9 is a schematic representation illustrating the structure of
the apparatus for detecting an end point of etching in the third
embodiment of the present invention,
FIG. 10 is a diagram representing output voltages of the
photoelectric converter at the time of multiple etching in the
apparatus shown in FIG. 9,
FIG. 11 is a diagram representing output waveforms of the pen
recorder at the time of multiple etching in the apparatus shown in
FIG. 9,
FIG. 12 is a schematic representation illustrating the structure of
the apparatus for detecting an end point of etching in the fourth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Since the etching treatment of a specimen, which is a wafer in this
case, is repeated in an etching treatment, the quantity of emission
collected from an etching chamber, namely an output (an electric
signal, in this case, being a voltage signal) of a photoelectric
converter shown in FIG. 2(b) becomes smaller than the output
obtainable at the time of initial treatment shown in FIG. 2(a). In
other words, output Va1 in the course of etching and output Vb1
after the termination thereof both being after time t1 (in this
case, a preset time after the etching began) in the treatment of
the first wafer (the initial treatment) as shown in FIG. 2(a) are
reduced to output Van in the course of etching and to output Vbn
after the termination thereof both being after time t1 in the
treatment of n wafer as shown in FIG. 2(b). Also, at the same time,
the differential value between output Va1 and output Vb1 at the
time of the first wafer treatment becomes smaller as in the case of
the differential value between Van and Vbn at the time n wafer
treatment. It is considered that this has been brought about by the
worsening condition of the plasma spectrum penetration in the
lighting section of the emission detector because of the repetitive
etching treatment which has caused a reactive product to adhere to
the surface of an inner wall of the treatment chamber. It has been
proven by the experiments by the inventor of the present invention
and some others that the following relationship can be established
between the outputs of the photoelectric converter in these
treatments of the first and n wafers: ##EQU1## The present
invention utilizes this relationship for detecting an end point of
etching accurately.
Now, the first embodiment of the present invention will be
described with reference to FIGS. 1, 2(a)-2(b), and 3-6.
One example of a means of detecting an end point of etching is
illustrated in FIG. 1. In an apparatus for etching treatment like,
for example, microwave etching apparatus 1, photoelectric converter
2 is provided in the section thereof to collect emission of plasma
spectrum. An output of photoelectric converter 2, which is a means
of converting electric signal, is transmitted through buffer 3 to
means of storage 12 and means of computing ratio 13 through A/D
converter 10. Another output of photoelectric converter 2 is
transmitted sequentially through subtracter 4 and gain amplifier 5
to means of detecting an end point of etching 11 and D/A converter
16 for an output signal of a corrected emission intensity, each
through A/D converter 10 respectively. A signal from D/A converter
16 will be output to a means of representation, for example pen
recorder 17.
Signals of gain setter 8 (for example, a variable resistor) and
offset setter 9 (for example, a variable resistor) are output to
means of storage 12 respectively through A/D converter 10. Another
signal of the side of gain setter 8 is output to gain amplifier 5.
Another signal of offset setter 9 is output to subtracter 4 through
D/A converter 7 for use of adjustment.
Means of storage 12 stores as input a direct output signal from
photoelectric converter 2, signals each from gain setter 8 and
offset setter 9, and a signal from means of computing correction
value 14 which will be explained later. Also, means of storage 12
outputs its stored contents to means of computing ratio 13 and
means of computing correction value 14.
Means of computing ratio 13 compares the output value of, for
example, the first specimen transmitted from photoelectric
converter 2, which has been stored in means of storage 12, and the
output value a subsequent specimen from photoelectric converter 2
and computes the ratio thereof. Also, means of computing ratio 13
will output the resulting ratio to means of computing correction
value 14. The ratio in this case is arrived at by Va1/Van . . . (2)
based on the previous expression (1).
Now, means of computing correction value 14 corrects offset and
gain values stored in means of storage 12 with a ratio worked out
by means of computing ratio 13, and computes new offset and gain
values. Also, means of computing correction value 14 will transmit
the new offset and gain values to D/A converter 7 and gain
amplifier 5. At the same time, the newly computed offset and gain
values will be transmitted to and stored in means 12. In this case,
the required values to be worked out will be arrived at as
follows:
Ordinarily, an output of photoelectric converter 2 as it is has too
small a differential value between the intensity of a signal in the
course of etching and that of a signal at the termination thereof.
It, therefore, becomes difficult to detect an end point of etching.
To counteract this, the output of photoelectric converter 2
(voltage signal) is offset and amplified in order to make greater
the differential value between the intensities of signals each in
the course of etching and at the termination thereof so that the
output can be corrected to detect the end point of etching easily.
In this respect, the offset and gain values to be amplified are set
initially, and the output value thus corrected will become as
represented in FIG. 3. FIG. 3 shows the change of an output voltage
(waveform of emission intensity) to pen recorder 17 in the first
wafer treatment.
Output voltage Vf1 shown in FIG. 3 is arrived at by offsetting the
photoelectric converter output shown in FIG. 2(a) with offset value
Voff1 (in the first wafer treatment) and amplifying, for example
with amplifying ratio G1 the differential value between the output
value thus offset and output Va1 in the course of etching after
time t1 has elapsed since the discharging began. Also output
voltage Vg1 shown in FIG. 3 is the value being arrived at by
amplifying with amplifying ratio G1 the differential value between
the offset value of the output and output Vb1 at the termination of
etching as shown in FIG. 2(a). The relative expression in this
respect is as follows:
Here, ordinarily, at the time of n wafer treatment the value thus
amplified with amplifying ratio G1 after having been offset with
offset value Voff1 becomes such an output voltage in time t1 as
shown in FIG. 4 and is reduced as compared with the output voltage
in the first wafer treatment as shown in FIG. 3. Therefore, as
shown in FIG. 4, the amplifying ratio will be modified after time
t1 so that output voltage Vfn can be amplified close to output
voltage Vf1 shown in FIG. 3. However, as shown in FIG. 2(b), the
differential value between outputs Van and Vbn of photoelectric
converter in n wafer treatment becomes smaller so that the
differential value between output voltage Vfn in the course of
etching and output voltage Vgn after etching will be smaller as
shown in FIG. 4 than that between Vf1 and Vg1 in the first wafer
treatment shown in FIG. 3 with the result that it becomes difficult
to detect the end point of etching.
To counteract this, according to the present invention, an
amplifying ratio (gain value) Gn in n wafer treatment is determined
by the following expression in accordance with a ratio obtainable
by the above-mentioned expression (2) at the time when n wafer is
treated. ##EQU2##
Then, offset value Voffn of n treatment is set so that output
voltage Vfn in n wafer treatment can be
The relative expression in this respect is as ##EQU3##
In this way, offset value Voffn and gain value Gn in n wafer
treatment can be computed by means of computing correction value
14, and both of them are established. As a result, output voltages
Vfn and Vgn to pen recorder 17 will be as follows: ##EQU4##
Now, the relationship among expression (3), (6), (8) can be
represented as follows: ##EQU5## Expression (8) can be:
Also, expression (10) can be reformulated: ##EQU6## Furthermore,
expression (1) can be reformulated: ##EQU7##
From expressions (12), (13), expression (9) can be reformulated as
follows: ##EQU8##
Consequently, expressions (3), (11) and expression (4), (14) can
be:
Vf1=Vfn
Vg1=Vgn
Thus, the output voltage after time t1 on pen recorder 17 in n
wafer treatment will be equal to the output voltage in the first
wafer treatment as shown in FIG. 5.
An offset value computed by means of computing correction value 14
is converted to the analog value by D/A converter 7 and transmitted
to subtracter 4. Thus, the offset value will reduce the output
value of photoelectric converter 2. Also, a gain value computed by
means of computing correction value 14 is transmitted to gain
amplifier 5. Thus, the output value from subtracter 4 is multiplied
by the gain value so that the output value of photoelectric
converter 2 can be corrected.
In this respect, means of correcting input value 6 comprises
subtracter 4 and gain amplifier 5. Also, means of detecting an end
point 11, means of storage 12, means of computing ratio 13, and
means of computing correction value 14 are defined as arithmetic
and memory circuits in microcomputer 15.
With an apparatus comprising as above, the detection of an end
point of etching will be conducted according to steps shown in FIG.
6.
First, prior to carrying on etching treatment continuously on a
wafer as a final product, an etching treatment will be conducted on
a sample wafer. Then, emission is collected and inputted after
being converted to an electric signal by photoelectric converter 2.
Simultaneously, offset setter 9 and gain setter 8 are adjusted
according to the waveform of an output voltage being shown on pen
recorder 17 in order to set the offset and gain values to generate
a waveform suitable for the detection of an end point of etching.
Thus, the setting is initialized (step 20 represents this).
Next, the actual output value from photoelectric converter 2 to
which the input was thus executed at the initialization will be
stored in means of storage 12, and at the same time, the offset and
gain values set at the initialization will be stored in means of
storage 12 (step 21 represents this). In this respect, it will
suffice for storage if the actual output value from photoelectric
converter 2 should be at least an output value to be stored at time
t1.
Next, the etching treatment of a wafer, which will be a final
product, is started (step 22 represents this). An emission in the
course of treatment is converted to an electric signal by
photoelectric converter 2, and transmitted to means of correcting
input 6. At this juncture, subtracter 4 and gain amplifier 5 will
be set to the offset and gain values stored in means of storage 12
at the time of initialization. The output of photoelectric
converter 2 is corrected by these correction values and then
transmitted to pen recorder 17 representing a waveform.
When a preset time t1 has elapsed after a wafer treatment began,
the other output of photoelectric converter 2 is inputted as it is
to means of computing ratio 13 (steps 23 and 24 represent this).
Ratio Va1/Van will be worked out through means of computing ratio
13 by comparison with the output value of photoelectric converter 2
at the time of initialization (step 25 represents this). Based on
this ratio, new offset value Voffn and gain value Gn are worked out
by means of computing correction value 14 (step 26 represents
this). With these new correction values, subtracter 4 and gain
amplifier 5 will be reset (step 27 represents this). Thus, the
value transmitted to means of detecting an end point 11 will become
the same as the value at the time of initialization.
At this juncture, the offset and gain values set at the time of
initialization are replaced by the new offset and gain values used
for resetting, and the new ones will be stored in means of storage
12 (step 28 represents this). In the next treatment, the electric
signal transmitted for a period up to time t1 will be corrected by
the new corrected value which has been reset.
In this way, with the electric signal which has been corrected to
be identical to the waveform at the time of initialization, an end
point of etching is detected by means of detecting an end point
with a known method thereof, for example, the one disclosed in U.S.
Pat. No. 4,615,761, using the secondary differentiation therein
(step 29 represents this).
When an end point has been detected, a signal to terminate the
etching is issued from means of detecting an end point 11 to stop
each power supply (microwave, magnetic coil, high-frequency power
source and others) of a microwave etching device 1 and supply of
treatment gas. Thus, a wafer treatment is terminated, and the wafer
thus treated will be transferred from the wafer treatment chamber
(step 30 represents this). If there is any new treatment of wafer,
the procedure will return to step 22, and if not, it terminates
there (step 31 represents this).
Now, according to the first embodiment of the present invention, a
correction value is computed by an output value of photoelectric
converter 2 which has been inputted thereto after a preset time t1
in the course of etching, and the output value of photoelectric
converter 2 can immediately be set to be equal to the emission
intensity at the time of initialization so as to obtain a waveform
of emission intensity on the same level of detection. There is,
thus, an effect of conducting the detection of an end point of
etching easily.
Also, the same waveform of an electric signal as the one corrected
at the time of initialization can be obtained at the time of each
treatment. Consequently, it becomes easy to detect an end point of
etching irrespective of the numbers of treatment and at the same
time, it is possible to detect an end point of etching accurately.
Thus, the detection of an end point of etching becomes constant
with the result that the quality of wafers in the same process can
be unified.
Also, even when the etching treatment is repeatedly carried out,
the detection of the end point thereof can be conducted without
fail. It, therefore, becomes unnecessary to do cleaning often so
that the lowering of throughput will be prevented.
According to the first embodiment of the present invention, the
initial values of offset and gain are set at the time of
initialization using a specimen as a sample. In this respect, any
specimen which will be a finished product can also be used.
Next, the second embodiment of the present invention will be
described with reference to FIGS. 2(a )-2(b) and 3-8, which uses a
different method of correcting offset and gain values from the
method previously described as an embodiment.
In FIG. 7, these members having the same reference numbers as in
FIG. 1 represent the same members and explanations will be omitted.
In FIG. 7, an output signal of photoelectric converter 2 is
transmitted to means of storage 12 and means of computing
correction value 14a through A/D converter 10 in order to obtain a
ratio between output signals in the course of etching and at the
termination thereof. Thus, this ratio is stored. This aspect is the
only point which differs from those described in FIG. 1. Means of
computing correction value 14a computes the ratio between outputs
Va1 and Vb1 of photoelectric converter 2 shown in FIG. 2(a). Said
ratio should be almost the same if the conditions of an etching
process and the specification of a specimen are constant. For
example, in case where an n wafer etching begins and time t1 has
elapsed (for example, a preset time after the etching began), means
of computing correction value 14a will work out corrected values of
gain and offset in accordance with said ratio and output Van shown
in FIG. 2(b), and output the corrected values to subtracter 4 and
gain amplifier 5 respectively. In this case, the treatment will be
as follows:
Gain value G is arrived at as follows: ##EQU9## Here, Vf1: The
value of output voltage at time t1 in the course of the first
etching as shown in FIG. 3.
Vg1: The value of output voltage at the termination of the first
etching as shown in FIG. 3.
K: Ratio Vb1/Va1 of the photoelectric converter output as shown in
FIG. 2(a) (being fixed in accordance with the specification of a
specimen and the conditions of etching process.)
Offset value Voff is arrived at as follows: ##EQU10##
Thus, the output to pen recorder 17 at the point of preset time t1
after etching began becomes Vf1, and also Vg1 after an end point of
etching has been detected.
Furthermore, even when the photoelectric converter output in the
course of n wafer treatment changes to be Van, Vbn as shown in FIG.
2(b), expression Vbn/Van=K is still obtainable if only the
conditions of an etching process and the specification of a
specimen are the same. Therefore, if gain value Gn and offset value
Voffn in the course of n wafer are: ##EQU11## Output Vfn of pen
recorder 17 at the point of time t1 shown in FIG. 5 will be the
same as output voltage Vf1 shown in FIG. 3. Also, output Vgn after
an end point of etching has been detected as shown in FIG. 5 will
be the same as output voltage Vg1 shown in FIG. 3 so that the same
waveform of emission intensity as the one in the course of the
first wafer treatment can be obtained.
With an apparatus comprising as above and steps shown in FIG. 8, an
end point of etching will be conducted. In FIG. 8, these having the
same reference numbers as in FIG. 6 represent the same steps, and
explanations are omitted. In FIG. 8, the ratio between output
values in the course of etching and at the termination thereof are
obtained by the output value of photoelectric converter 2 at the
time of initialization, and said ratio and the offset and gain
values will be stored in means of storage 12 (step 21a represents
this). This is a point which differs from those steps shown in FIG.
6. Also, in case where a wafer is treated as a final product, the
new values of gain and offset will be worked out by the ratio
between the output values of photoelectric converter 2 inputted at
the point of preset time (t1) and at the time of initialization
(step 26a represents this). This is another point which differs
from those steps shown in FIG. 6.
According to the second embodiment of the present invention, the
same effect as referred to in an embodiment described as the first
embodiment thereof is attainable.
Now, these first and second embodiments describe the case where the
quantity of an emission increases in the course of etching (namely
the waveform of emission intensity represent shape upwardly), but
they may satisfactorily be to the case where the quantity of an
emission decreases in the course of etching (namely, the waveform
of emission intensity representing shape.)
Also, these first and second embodiment the case where a plurality
of wafers are treated under the same process, but they may
satisfactorily be applicable to the cases of a multiple etching
treatment in which the process changes in the course of treating
the same wafer or a wafer treatment in which the specification of a
specimen and the conditions of an etching process change in the
same device of treatment if only a plurality of wafers are treated
under the same conditions.
Now, a multiple etching treatment in which the process changes in
the course of the same wafer treatment will be exemplified and
explained as the third embodiment of the present invention with
reference to FIGS. 9 to 11.
FIG. 9 is a schematic representation of the construction of an
apparatus for detecting an end point of etching shown in FIG. 1.
The apparatus for detecting an end point of etching comprises
photoelectric converter 2a, offset adjuster 4a, gain adjuster 5a,
arithmetic and memory circuit 15a, pen recorder 17a, gain setter
8a, and offset setter 9a. In this case, an offset value and again
value in each step of multiple etching are set by offset setter 9a
and gain setter 8a. Said offset and gain values thus set in each
step are inputted and stored in arithmetic and memory circuit 15a.
Also, an actual output (a voltage signal) of photoelectric
converter 2a and a voltage signal sequentially output through
offset adjuster 4a and gain adjuster 5a are inputted in arithmetic
and memory circuit 15a. Arithmetic and memory circuit 15a outputs
to offset adjuster 4a an offset value set by offset setter 9a or an
offset value worked out in such a manner as has been explained in
the first and second embodiments. Also, simultaneously, arithmetic
and memory circuit 15a outputs to gain adjuster 5a a gain value set
by gain setter 8a or a gain value worked out in such a manner as
has been explained in the first and second embodiments.
Furthermore, arithmetic and memory circuit 15a detects an end point
of etching by an electric signal being sequentially output through
offset adjuster 4a and gain adjuster 5a. Offset adjuster 4a
subtracts an actual electric signal output from photoelectric
converter 2a by an offset value being output from arithmetic and
memory circuit 15a. Gain adjuster 5a multiplies said electric
signal thus subtracted by a gain value being output from arithmetic
and memory circuit 15a. Also, in the third embodiment of the
present invention, the setting means 18, which will replace and
reset the setting values of gain setter 8a and offset setter 9a, is
provided in addition to an apparatus for detecting an end point of
etching comprising the same as in FIG. 1.
In FIG. 10, an actual waveform of emission intensity is shown for a
multiple etching, for example, the one with a three-step etching in
an apparatus being constructed as above. Output voltages prior to
the termination of etching (dead time t1) and after the termination
thereof in step 1 will be V1 and V2. In step 2, output voltages
prior to the termination of etching (dead time t2) and after the
termination thereof will be V3 and V4. In step 3, output voltages
prior to the termination of etching (dead time t3) and after the
termination thereof will be V5 and V6. In this way, actual
waveforms of emission intensity of the multiple etching vary in
each step respectively.
Therefore, as shown in FIG. 11, each waveform of output to pen
recorder 17a in each step is made to be identical in order to
facilitate detecting an end point of etching therein. First, in
step 1, values of offset and gain are adjusted and set so that an
output waveform at the point of time t1 in step 1 will be made to
detect an end point of etching easily. Next, in step 2, the values
of gain and offset are adjusted and set so as to make the output
waveform at the point of time t2 identical to the waveform set in
step 1. Also, in step 3, the adjustment and setting are carried out
as in step 2. The gain and offset values thus set in each step are
replaced and reset by setting means 18 and are replaced by setting
means 18 with a setting value in next step by, for example, time
t1, t2, t3 or a present time after an end point of previous etching
has been detected.
As has been described, according to the third embodiment of the
present invention, the waveform whereby to detect an end point of
etching in each step can be made to have a value of the same level.
Thus, the detection of an end point of etching is facilitated.
Also, in the treatment of the second wafer and on, the offset and
gain settings are conducted in each step while they are being
corrected in the same manner as in the first and second
embodiments, making it possible to detect an end point of etching
efficiently irrespective of numbers of wafers to be treated.
Now, the replacement and resetting of gain and offset values may be
conducted by the replacement and reading out by, for example,
setting time (t1, t2, t3) and others after respective values having
been stored in arithmetic and memory circuit 15a.
Also, the third embodiment of the present invention describes the
case of multiple etching treatment in which process changes in the
same wafer treatment but even in case of the wafer etching
treatment where the specification of a wafer and the conditions of
etching process change in the same treatment apparatus, it is
possible to detect an end point of etching the same as in the first
and second embodiments. In other words, instead of the
aforementioned steps, the setting of offset and gain values are
conducted by gain setter 8a and offset setter 9a according to each
specification of a wafer or conditions of etching process. Said
setting values are changed by setting means 18 in accordance with
changes in the specification of a wafer and the conditions of
etching process. Thus inputting the specification of a wafer and
the conditions of etching process enables the functions of
automatic gain and offset to work as in the first and second
embodiments, making it easy to detect an end point of etching of
the specimen, although the specification and conditions of process
thereof change.
In these first, second, and third embodiments, the correction of
emission intensity is made by offset and gain values in order to
detect an end point of etching, but the correction of an amplifying
ratio of the photoelectric converter may also be applicable. The
construction of an apparatus in this case will be described with
reference to FIG. 12 as the fourth embodiment of the present
invention.
In FIG. 12, these members having the same reference numbers as in
FIG. 9 represent the same members, and explanations are omitted. In
FIG. 12, the first point which differs from FIG. 9 is that the
amplifying ratio of photoelectric converter 2b becomes obtainable.
Also, the second point of difference is that arithmetic and memory
circuit 15b compares as in the first embodiment a corresponding
emission intensity in the course of etching treatment (an actual
output of photoelectric converter 2b in the course of etching) with
the emission intensity stored at the time of initialization (an
actual output of photoelectric converter 2b at the time of
initialization), and works out a new amplifying ratio of
photoelectric converter 2b to correct the amplifying ratio of
photoelectric converter 2b.
In an apparatus thus constructed, while an offset value and a gain
value at the time of initialization remain as they are, the
amplifying ratio of photoelectric converter 2b can be corrected.
Thus, the waveform of emission intensity can be obtained as in the
first embodiment to detect an end point of etching, making it
possible to carry out the detection on the same level.
Therefore, according to the fourth embodiment of the present
invention, the same effect as in the first embodiment is
attainable.
As has been explained, according to the present invention, it is
possible to detect an end point of etching as easy as to do the
same at the time of initialization, even when an etching treatment
is repeatedly carried out, resulting in the reduction of quantity
of emission obtainable from the member of emission detecting.
Also, in each step of a multiple etching, the functions of
automatic gain and offset can be utilized so as to facilitate
detecting an end point of etching easily.
Furthermore, as inputting the specification of a specimen and the
conditions of etching process enables the functions of automatic
gain and offset to work, it is possible to detect easily an end
point of etching of the specimen, although the specification and
conditions of process thereof change.
* * * * *